The present invention relates to a method and apparatus for producing oil and gas, and particularly to a method and apparatus for efficiently and effectively removing cormate or interstitial water from oil and gas wells.
Oil and gas are produced from wells penetrating subsurface hydrocarbon-bearing formations or reservoirs. Such reservoirs can be found at various depths in the earth's subsurface. In gas-producing reservoirs, the gas contained therein is compressed by the weight of the overlying earth. When the formation is breached by a well, the gas tends to flow into the well under formation pressure. Any other fluid in the formation, such as connate water trapped in the interstices of the sediments at the time the formation was deposited, also moves toward the well. Production of the fluids is maintained as long as the pressure in the well is less than the formation pressure. Eventually production ceases either because formation pressure equals or exceeds bore hole pressure. In the latter case, it has often been found that cormate or interstitial water filling the well exerts sufficient pressure to stop or sharply reduce production. A problem arises when the expense of removing the water becomes a substantial portion of, or exceeds the value of the hydrocarbon produced.
Several kinds of lift or pumping devices have been used to extract fluids from wells. Piston pumps are common and require either an electric or gas powered motor which is coupled by belts or gears to a reciprocating pump jack. The reciprocating motion of the pump jack, in turn, reciprocates a piston within a cylinder disposed within the well. As the piston reciprocates within the well, valves open and close, creating a low pressure in the well and drawing the oil to the surface. Centrifugal or rotary pumps, often found in water wells, also operate by either an electric or gas powered motor. Usually, the pump is attached directly to the shaft of the motor. The rotary motion of the veins creates a low pressure in the well, thereby causing the fluid to flow up the well.
A major disadvantage with both piston and centrifugal pumps is the mechanical fatigue and failure of moving parts which require continual maintenance and repair. Furthermore, such systems are consumers of energy, that is, they use electricity or burn fuel costing many times more to run than passive systems. Typically, the expense of maintaining and operating such systems will eventually exceed the economic benefits returned.
In the singular case of oil wells, gas-lift systems have been used wherein gas from the well, an air compressor, or other source of gas is injected down the well through a pipe coupled to a second pipe having an end immersed in the oil. The injection of a volume of gas below a volume of oil in the pipe lifts the oil to the surface. Gas-lift systems, which use an air compressor or other mechanical device located at the well site to inject the gas, also require periodic service and maintenance and thus suffer the same disadvantages as the mechanical pumps described above. Gas-lift systems which use the gas produced from the well are expensive and difficult to install since the gas producing formation must be physically separated from the oil producing formation by at least one packing device. Such systems are typically permanent and are expensive to remove or service. Moreover, systems using formation gas are only effective so long as gas is being produced from the well; otherwise, an external source of gas is necessary. Lastly, many of the gas-lift systems corrode because they are made from materials unsuitable for the well environment. This is undesirable and can eventually lead to failure of the complete system.
Because of the ever increasing cost associated with the production of hydrocarbon resources, there has been, and continues to be a long-felt need for a low maintenance gas-lift assembly to more fully develop hydrocarbon resources. Moreover, such a device should be able to operate at a fraction of the cost of previous systems.